CN114577623B - Evaluation method for mechanical properties of lithium battery foil - Google Patents

Evaluation method for mechanical properties of lithium battery foil Download PDF

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Publication number
CN114577623B
CN114577623B CN202210192268.4A CN202210192268A CN114577623B CN 114577623 B CN114577623 B CN 114577623B CN 202210192268 A CN202210192268 A CN 202210192268A CN 114577623 B CN114577623 B CN 114577623B
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Prior art keywords
battery cell
foil
pole piece
mechanical properties
thermal expansion
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CN202210192268.4A
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CN114577623A (en
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邱申保
赵悠曼
周崇旺
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Dongguan Chuangming Battery Technology Co Ltd
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Dongguan Chuangming Battery Technology Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
    • G01N3/18—Performing tests at high or low temperatures
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D1/00—Processes for applying liquids or other fluent materials
    • B05D1/36—Successively applying liquids or other fluent materials, e.g. without intermediate treatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
    • B05D3/02—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by baking
    • B05D3/0254—After-treatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
    • B05D7/14—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
    • B05D7/50—Multilayers
    • B05D7/52—Two layers
    • B05D7/54—No clear coat specified
    • B05D7/542—No clear coat specified the two layers being cured or baked together
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
    • G01N1/286—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q involving mechanical work, e.g. chopping, disintegrating, compacting, homogenising
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/003—Generation of the force
    • G01N2203/0057—Generation of the force using stresses due to heating, e.g. conductive heating, radiative heating
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0058—Kind of property studied
    • G01N2203/006—Crack, flaws, fracture or rupture
    • G01N2203/0067—Fracture or rupture
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02—Details not specific for a particular testing method
    • G01N2203/0202—Control of the test
    • G01N2203/0212—Theories, calculations
    • G01N2203/0214—Calculations a priori without experimental data
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02—Details not specific for a particular testing method
    • G01N2203/022—Environment of the test
    • G01N2203/0222—Temperature
    • G01N2203/0226—High temperature; Heating means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02—Details not specific for a particular testing method
    • G01N2203/026—Specifications of the specimen
    • G01N2203/0262—Shape of the specimen
    • G01N2203/0278—Thin specimens
    • G01N2203/0282—Two dimensional, e.g. tapes, webs, sheets, strips, disks or membranes
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02—Details not specific for a particular testing method
    • G01N2203/06—Indicating or recording means; Sensing means
    • G01N2203/067—Parameter measured for estimating the property
    • G01N2203/0694—Temperature
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention relates to the technical field of batteries, and discloses a method for evaluating mechanical properties of lithium battery foil, which comprises the following steps: providing a battery cell group comprising a plurality of battery cells, wherein a pole piece of each battery cell comprises a foil to be evaluated and an active material coating layer coated on the surface of the foil to be evaluated, and the outer surface of the active material coating layer is also coated with a thermal expansion material coating layer; baking the battery cell group in a preset temperature range, wherein the baking temperature of each battery cell is different, so that the thermal expansion material coating layers of each battery cell are expanded to different states; and obtaining the pole piece state of each battery cell, and evaluating the mechanical properties of the foil to be evaluated according to the pole piece state. According to the embodiment of the invention, the actual use scene of the foil is simulated, so that the actual test requirement can be met, the baking process is adopted to replace the conventional charge and discharge process, the pole piece states under different expansion rates can be obtained in a short time, the evaluation period is greatly shortened, and the occupation of test resources is reduced.

Description

Evaluation method for mechanical properties of lithium battery foil
Technical Field
The invention relates to the technical field of batteries, in particular to a method for evaluating mechanical properties of lithium battery foil.
Background
Currently, a tensile machine is generally used to perform longitudinal or transverse unidirectional stretching on a foil with a specific size, and the tensile strength and the elongation of the foil in the longitudinal or transverse direction are measured, so that the mechanical properties of the foil are evaluated.
In fact, during actual use of lithium battery foils, physical failure (cracking or even breaking) phenomena often occur during charging and discharging of lithium batteries. The positive and negative electrode plates made of the foil materials can correspondingly expand and contract in volume along with the cyclic charge and discharge of the battery, and particularly, the volume expansion of the battery under a high nickel/silicon system is obvious, the foil materials can be subjected to radial expansion stress and tangential tensile stress, and therefore the foil materials are more prone to fracture.
However, the test result obtained by the tensile machine only reflects the mechanical properties of the foil when the foil is subjected to unidirectional tensile force, but cannot reflect the mechanical properties of the foil when the foil is subjected to radial expansion stress and tangential tensile stress, and cannot meet the actual test requirements.
Therefore, in order to evaluate the physical failure phenomenon of the foil in the charge-discharge process, a method of disassembling and judging the battery in the cyclic charge-discharge process is often adopted, but the method requires long test time due to continuous charge-discharge of the battery, occupies more test resources, and cannot meet the requirements of rapid development and application.
Disclosure of Invention
The invention aims to provide an evaluation method of mechanical properties of a lithium battery foil, which aims to overcome the defects of long test period and more occupied test resources in the prior art.
To achieve the purpose, the invention adopts the following technical scheme:
a method of evaluating mechanical properties of a lithium battery foil, comprising:
providing a battery cell group comprising a plurality of battery cells, wherein a pole piece of each battery cell comprises a foil to be evaluated and an active material coating layer coated on the surface of the foil to be evaluated, and the outer surface of each active material coating layer is also coated with a thermal expansion material coating layer;
baking the battery cell group in a preset temperature range, wherein the baking temperature of each battery cell is different, so that the thermal expansion material coating layers of the battery cells are expanded to different states;
and acquiring the pole piece state of each battery cell, and evaluating the mechanical properties of the foil to be evaluated according to the pole piece state.
Optionally, the processing method of the battery cell includes:
coating active materials on the front and back surfaces of the foil to be evaluated, and rolling to form active material coating layers to obtain the pole piece; and coating a thermal expansion material on the outer surface of the pole piece and curing to form the thermal expansion material coating layer.
Optionally, the processing method of the battery cell further includes:
and assembling the pole piece and the diaphragm, wherein the surface of the pole piece is coated with the coating layer of the thermal expansion material, packaging, and then injecting electrolyte to obtain the battery cell.
Optionally, the thermal expansion material is silicon rubber with a thermal expansion coefficient larger than a preset value.
Optionally, the silicone rubber comprises an A component and a B component, and the mixing ratio of the A component to the B component is 10:1.
Optionally, the step of coating the silicone rubber on the outer surface of the pole piece and curing includes:
uniformly coating the component A on the outer surface of the pole piece, wherein the coating thickness is 50-200 mu m; and uniformly coating the B component on the outer surface of the A component, wherein the coating thickness is 10-30 mu m.
Optionally, the assembly ratio of the battery cell is 50% -80% before the coating layer of the thermal expansion material is formed.
Optionally, after the coating layer of the thermal expansion material is formed, the assembly ratio of the battery cell is 95% or more.
Optionally, the obtaining the pole piece state of each battery cell includes: and disassembling each battery cell, and checking whether the pole piece of each battery cell is cracked or broken.
Optionally, the preset temperature range is determined according to an initial volume, a linear expansion coefficient, a volume expansion coefficient of the thermal expansion material coating layer, and an operating temperature range of the constituent units of the battery cell except for the thermal expansion material coating layer.
Compared with the prior art, the embodiment of the invention has the following beneficial effects:
according to the embodiment of the invention, the thermal expansion material coating is introduced into the pole piece, and the thermal expansion material coating is expanded in a baking mode, so that radial expansion stress and tangential tensile stress in an actual charge-discharge environment are generated on the foil, the state of the foil in evaluation can be basically consistent with the actual application state, and finally the accuracy of the mechanical property evaluation result is effectively ensured.
Compared with the traditional mode, the embodiment of the invention not only simulates the actual use scene of the foil, thereby meeting the actual test requirement, but also adopts the baking process to replace the conventional charge and discharge process, thereby obtaining the pole piece states under different expansion rates in a short time, greatly shortening the evaluation period and reducing the occupation of test resources.
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions of the prior art, the drawings which are used in the description of the embodiments or the prior art will be briefly described, it being obvious that the drawings in the description below are only some embodiments of the invention, and that other drawings can be obtained from these drawings without inventive faculty for a person skilled in the art.
Fig. 1 is a flowchart of an evaluation method for mechanical properties of a lithium battery foil according to an embodiment of the present invention.
Fig. 2 is a flowchart of a processing method of a battery cell according to an embodiment of the present invention.
Detailed Description
In order to make the objects, features and advantages of the present invention more comprehensible, the technical solutions in the embodiments of the present invention are described in detail below with reference to the accompanying drawings, and it is apparent that the embodiments described below are only some embodiments of the present invention, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In order to solve the problems that the foil test scene is inconsistent with the actual use scene in the existing tensile machine test mode, and the existing cyclic charge-discharge disassembly mode has long test period and occupies more test resources, the embodiment of the invention provides a method for evaluating the mechanical properties of the lithium battery foil, which can construct a simulation scene very similar to the actual use scene of the foil, and complete mechanical property evaluation in a simple baking mode at the foil in the simulation scene, thereby simultaneously solving the various problems.
Referring to fig. 1, the method for evaluating mechanical properties of a lithium battery foil according to an embodiment of the present invention includes the steps of:
step 101, providing a battery cell group comprising a plurality of battery cells, wherein a pole piece of each battery cell comprises a foil to be evaluated and an active material coating layer coated on the surface of the foil to be evaluated, and the outer surface of the active material coating layer is also coated with a thermal expansion material coating layer.
In the battery cell of the embodiment of the invention, the outer surface of the pole piece is also uniformly coated with a thermal expansion material coating layer, unlike a conventional battery cell. The coating layer of the thermal expansion material has thermal expansion performance, and various materials with good thermal expansion performance, reliability and stability can be selected and used.
The thermal expansion material coating layer has the following functions: the foil is expanded after being heated, radial expansion stress and tangential tensile stress are generated on the foil attached to the foil, so that the state of the foil in the current testing environment is basically the same as the state of the foil in the actual use environment, and the accuracy of an evaluation result is ensured.
Step 102, baking the battery cell group in a preset temperature range, wherein the baking temperatures of the battery cells are different, so that the thermal expansion material coating layers of the battery cells are expanded to different states.
In order to improve the test efficiency, a reasonable preset temperature range can be selected according to an empirical value, and each battery cell in the battery cell group is baked with different temperature gradients in the range, so that each battery cell reaches an expansion state basically consistent with different charge and discharge stages, and a plurality of detection samples in different states can be obtained.
Specifically, the preset temperature range may be determined according to the initial volume, the linear expansion coefficient, and the volume expansion coefficient of the coating layer of the thermal expansion material, and the operating temperature range of the constituent units (such as the diaphragm) of the battery cell except for the coating layer of the thermal expansion material (typically, the operating temperature of the diaphragm is 130 ℃ or less).
And 103, acquiring the pole piece state of each battery cell, and evaluating the mechanical properties of the foil to be evaluated according to the pole piece state.
Exemplary, the method for obtaining the pole piece state of each cell includes: and disassembling each battery cell, checking whether the pole piece of each battery cell is cracked or broken, and determining the state of the pole piece according to the state. Based on the above, the baking temperature value for converting the uncracked state of the pole piece into the cracked state can be determined by comparing the states of the pole pieces, and then the mechanical property of the foil can be evaluated according to the thermal expansion coefficient of the coating layer combined with the thermal expansion material.
Taking a thermal expansion material coating layer as silicon rubber as an example, setting the initial temperature as T0, the oven temperature as T, the initial volume of the silicon rubber as V0, and the heated volume as V, wherein V=v0 (1+βΔT) ≡v0 (1+3αΔT), and the α and β respectively represent the linear expansion coefficient and the volume expansion coefficient of the silicon rubber. The volume expansion coefficient beta of the R10301 silicone rubber is about 9.13 x 10 -4/ The volume expansion rate of the silicone rubber is generally more than 10 percent at the temperature.
According to the evaluation method, the thermal expansion material coating is introduced into the pole piece, and then the thermal expansion material coating can be expanded in a baking mode, so that radial expansion stress and tangential tensile stress in an actual charge-discharge environment are generated on the foil, the state of the foil in evaluation can be basically consistent with the actual application state, and finally the accuracy of the mechanical property evaluation result is effectively ensured.
Compared with the traditional mode, the embodiment of the invention not only simulates the actual use scene of the foil, thereby meeting the actual test requirement, but also adopts the baking process to replace the conventional charge and discharge process, thereby obtaining the pole piece state under different expansion rates in a short time and greatly shortening the evaluation period.
In order to further improve accuracy of the evaluation result, referring to fig. 2, in the embodiment of the present invention, the battery cell for testing may be prepared by the following method:
and 201, coating active materials on the front and back surfaces of the foil to be evaluated, and rolling to form active material coating layers to obtain the pole piece.
In this step, the slurry may be prepared and coated according to a conventional process, which is not limited in the embodiment of the present invention.
Illustratively, the compounding method is: the electrode raw materials, including active materials, inactive materials, binders and solvents are prepared into slurry meeting the requirements of viscosity and solid content in a certain proportion, and the anode and the cathode are required to be respectively and independently mixed.
The coating method comprises the following steps: and uniformly coating the slurry on the front and back sides of the foil to be evaluated by a coating machine according to the technical requirements, so that the anode slurry is coated on the aluminum foil, the cathode slurry is coated on the copper foil, and the anode and the cathode are required to be coated independently.
And 202, coating a thermal expansion material on the outer surface of the pole piece and curing to form a thermal expansion material coating layer.
The thermal expansion material is illustratively a silicone rubber having a coefficient of thermal expansion greater than a predetermined value. Taking R10301 silicone rubber as an example, the silicone rubber comprises an A component and a B component, and the mixing ratio of the A component and the B component is 10:1. In this regard, the method of coating the silicone rubber on the outer surface of the pole piece and curing may be: uniformly coating the component A on the outer surface of the pole piece, wherein the coating thickness is 50-200 mu m; and uniformly coating the outer surface of the component A with the coating thickness of 10-30 mu m.
The assembly ratio of the battery cell is preferably 50% -80% before forming the thermal expansion material coating layer, and enough coating space is reserved for the thermal expansion material coating layer; after the formation of the coating layer of the thermally expansive material, the assembly ratio of the battery cells is preferably 95% or more.
And 203, assembling the pole piece with the surface coated with the coating layer of the thermal expansion material and the diaphragm, packaging, and then injecting electrolyte to obtain the battery cell.
According to the method, besides the coating layer of the thermal expansion material is added, the foil to be evaluated is manufactured into the battery core to be tested according to conventional coating, assembling, packaging and liquid injection operations, so that the test environment of the foil to be evaluated is more similar to an actual application scene, and the accuracy of an evaluation result can be effectively improved; meanwhile, compared with the conventional manufacturing process of the battery cell, the manufacturing process reduces the procedures of formation and the like, so that the evaluation efficiency is improved and the evaluation cost is reduced on the basis of not influencing the accuracy of a test result.
The above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. The method for evaluating the mechanical properties of the lithium battery foil is characterized by comprising the following steps of:
providing a battery cell group comprising a plurality of battery cells, wherein a pole piece of each battery cell comprises a foil to be evaluated and an active material coating layer coated on the surface of the foil to be evaluated, and the outer surface of each active material coating layer is also coated with a thermal expansion material coating layer;
baking the battery cell group in a preset temperature range, wherein the baking temperature of each battery cell is different, so that the thermal expansion material coating layers of the battery cells are expanded to different states;
and acquiring the pole piece state of each battery cell, and evaluating the mechanical properties of the foil to be evaluated according to the pole piece state.
2. The method for evaluating mechanical properties of a lithium battery foil according to claim 1, wherein the processing method of the battery cell comprises:
coating active materials on the front and back surfaces of the foil to be evaluated, and rolling to form active material coating layers to obtain the pole piece; and coating a thermal expansion material on the outer surface of the pole piece and curing to form the thermal expansion material coating layer.
3. The method for evaluating mechanical properties of a lithium battery foil according to claim 2, wherein the method for processing the battery cell further comprises:
and assembling the pole piece and the diaphragm, wherein the surface of the pole piece is coated with the coating layer of the thermal expansion material, packaging, and then injecting electrolyte to obtain the battery cell.
4. A method of evaluating mechanical properties of a lithium battery foil according to any one of claims 2 to 3, wherein the thermally expansive material is a silicone rubber having a coefficient of thermal expansion greater than a preset value.
5. The method for evaluating mechanical properties of a lithium battery foil according to claim 4, wherein the silicone rubber comprises an a-component and a B-component, and a mixing ratio of the a-component and the B-component is 10:1.
6. The method of evaluating mechanical properties of a lithium battery foil according to claim 5, wherein the step of coating the silicone rubber on the outer surface of the pole piece and curing comprises:
uniformly coating the component A on the outer surface of the pole piece, wherein the coating thickness is 50-200 mu m; and uniformly coating the B component on the outer surface of the A component, wherein the coating thickness is 10-30 mu m.
7. The method of evaluating mechanical properties of a lithium battery foil according to claim 2, wherein the electrical core is assembled at a ratio of 50% -80% before the coating layer of the thermal expansion material is formed.
8. The method of evaluating mechanical properties of a lithium battery foil according to claim 7, wherein a packaging ratio of the battery cell after the formation of the coating layer of the thermal expansion material is 95% or more.
9. The method for evaluating mechanical properties of a lithium battery foil according to claim 1, wherein the obtaining the pole piece state of each of the battery cells comprises:
and disassembling each battery cell, and checking whether the pole piece of each battery cell is cracked or broken.
10. The method of evaluating mechanical properties of a lithium battery foil according to claim 1, wherein the preset temperature range is determined according to an initial volume of the thermally expansive material coating, a linear expansion coefficient, a bulk expansion coefficient, and an operating temperature range of constituent units of the battery cell other than the thermally expansive material coating.
CN202210192268.4A 2022-02-28 2022-02-28 Evaluation method for mechanical properties of lithium battery foil Active CN114577623B (en)

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